Re: [PATCH 23/26] ib: Convert qib_get_user_pages() toget_user_pages_unlocked()

From: Jan Kara
Date: Wed Oct 16 2013 - 17:40:12 EST

On Tue 08-10-13 21:06:04, Jan Kara wrote:
> On Mon 07-10-13 19:26:04, Jan Kara wrote:
> > On Mon 07-10-13 15:38:24, Marciniszyn, Mike wrote:
> > > > > This patch and the sibling ipath patch will nominally take the mmap_sem
> > > > > twice where the old routine only took it once. This is a performance
> > > > > issue.
> > > > It will take mmap_sem only once during normal operation. Only if
> > > > get_user_pages_unlocked() fail, we have to take mmap_sem again to undo
> > > > the change of mm->pinned_vm.
> > > >
> > > > > Is the intent here to deprecate get_user_pages()?
> > >
> > > The old code looked like:
> > > __qib_get_user_pages()
> > > (broken) ulimit test
> > > for (...)
> > > get_user_pages()
> > >
> > > qib_get_user_pages()
> > > mmap_sem lock
> > > __qib_get_user_pages()
> > > mmap_sem() unlock
> > >
> > > The new code is:
> > >
> > > get_user_pages_unlocked()
> > > mmap_sem lock
> > > get_user_pages()
> > > mmap_sem unlock
> > >
> > > qib_get_user_pages()
> > > mmap_sem lock
> > > ulimit test and locked pages maintenance
> > > mmap_sem unlock
> > > for (...)
> > > get_user_pages_unlocked()
> > >
> > > I count an additional pair of mmap_sem transactions in the normal case.
> > Ah, sorry, you are right.
> >
> > > > > Could the lock limit test be pushed into another version of the
> > > > > wrapper so that there is only one set of mmap_sem transactions?
> > > > I'm sorry, I don't understand what you mean here...
> > > >
> > >
> > > This is what I had in mind:
> > >
> > > get_user_pages_ulimit_unlocked()
> > > mmap_sem lock
> > > ulimit test and locked pages maintenance (from qib/ipath)
> > > for (...)
> > > get_user_pages_unlocked()
> > > mmap_sem unlock
> > >
> > > qib_get_user_pages()
> > > get_user_pages_ulimit_unlocked()
> > >
> > > This really pushes the code into a new wrapper common to ipath/qib and
> > > any others that might want to combine locking with ulimit enforcement.
> > We could do that but frankly, I'd rather change ulimit enforcement to not
> > require mmap_sem and use atomic counter instead. I'll see what I can do.
> OK, so something like the attached patch (compile tested only). What do
> you think? I'm just not 100% sure removing mmap_sem surrounding stuff like
> __ipath_release_user_pages() is safe. I don't see a reason why it shouldn't
> be - we have references to the pages and we only mark them dirty and put the
> reference - but maybe I miss something subtle...
Ping? Any opinion on this?

Honza

> From 44fe90e8303b293370f077ae665d6e43846cf277 Mon Sep 17 00:00:00 2001
> From: Jan Kara <jack@xxxxxxx>
> Date: Tue, 8 Oct 2013 14:16:24 +0200
> Subject: [PATCH] mm: Switch mm->pinned_vm to atomic_long_t
>
> Currently updates to mm->pinned_vm were protected by mmap_sem.
> kernel/events/core.c actually held it only for reading so that may have
> been racy. The only other user - Infiniband - used mmap_sem for writing
> but it caused quite some complications to it.
>
> So switch mm->pinned_vm and convert all the places using it. This allows
> quite some simplifications to Infiniband code and it now doesn't have to
> care about mmap_sem at all.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> drivers/infiniband/core/umem.c | 56 +++------------------
> drivers/infiniband/core/uverbs_cmd.c | 1 -
> drivers/infiniband/core/uverbs_main.c | 2 -
> drivers/infiniband/hw/ipath/ipath_file_ops.c | 2 +-
> drivers/infiniband/hw/ipath/ipath_kernel.h | 1 -
> drivers/infiniband/hw/ipath/ipath_user_pages.c | 70 +++-----------------------
> drivers/infiniband/hw/qib/qib_user_pages.c | 20 ++------
> fs/proc/task_mmu.c | 2 +-
> include/linux/mm_types.h | 2 +-
> include/rdma/ib_umem.h | 3 --
> include/rdma/ib_verbs.h | 1 -
> kernel/events/core.c | 13 +++--
> 12 files changed, 29 insertions(+), 144 deletions(-)
>
> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> index 0640a89021a9..294d2e468177 100644
> --- a/drivers/infiniband/core/umem.c
> +++ b/drivers/infiniband/core/umem.c
> @@ -80,6 +80,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
> {
> struct ib_umem *umem;
> struct page **page_list;
> + struct mm_struct *mm = current->mm;
> struct ib_umem_chunk *chunk;
> unsigned long locked;
> unsigned long lock_limit;
> @@ -126,20 +127,13 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
>
> npages = PAGE_ALIGN(size + umem->offset) >> PAGE_SHIFT;
>
> - down_write(&current->mm->mmap_sem);
> -
> lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> locked = npages;
> - if (npages + current->mm->pinned_vm > lock_limit &&
> + if (atomic_long_add_return(&mm->pinned_vm, npages) > lock_limit &&
> !capable(CAP_IPC_LOCK)) {
> - up_write(&current->mm->mmap_sem);
> - kfree(umem);
> - free_page((unsigned long) page_list);
> - return ERR_PTR(-ENOMEM);
> + ret = -ENOMEM;
> + goto out;
> }
> - current->mm->pinned_vm += npages;
> -
> - up_write(&current->mm->mmap_sem);
>
> cur_base = addr & PAGE_MASK;
>
> @@ -201,9 +195,7 @@ out:
> if (ret < 0) {
> __ib_umem_release(context->device, umem, 0);
> kfree(umem);
> - down_write(&current->mm->mmap_sem);
> - current->mm->pinned_vm -= locked;
> - up_write(&current->mm->mmap_sem);
> + atomic_long_sub(&mm->pinned_vm, locked);
> }
> free_page((unsigned long) page_list);
>
> @@ -211,17 +203,6 @@ out:
> }
> EXPORT_SYMBOL(ib_umem_get);
>
> -static void ib_umem_account(struct work_struct *work)
> -{
> - struct ib_umem *umem = container_of(work, struct ib_umem, work);
> -
> - down_write(&umem->mm->mmap_sem);
> - umem->mm->pinned_vm -= umem->diff;
> - up_write(&umem->mm->mmap_sem);
> - mmput(umem->mm);
> - kfree(umem);
> -}
> -
> /**
> * ib_umem_release - release memory pinned with ib_umem_get
> * @umem: umem struct to release
> @@ -234,37 +215,14 @@ void ib_umem_release(struct ib_umem *umem)
>
> __ib_umem_release(umem->context->device, umem, 1);
>
> - mm = get_task_mm(current);
> + mm = current->mm;
> if (!mm) {
> kfree(umem);
> return;
> }
>
> diff = PAGE_ALIGN(umem->length + umem->offset) >> PAGE_SHIFT;
> -
> - /*
> - * We may be called with the mm's mmap_sem already held. This
> - * can happen when a userspace munmap() is the call that drops
> - * the last reference to our file and calls our release
> - * method. If there are memory regions to destroy, we'll end
> - * up here and not be able to take the mmap_sem. In that case
> - * we defer the vm_locked accounting to the system workqueue.
> - */
> - if (context->closing) {
> - if (!down_write_trylock(&mm->mmap_sem)) {
> - INIT_WORK(&umem->work, ib_umem_account);
> - umem->mm = mm;
> - umem->diff = diff;
> -
> - queue_work(ib_wq, &umem->work);
> - return;
> - }
> - } else
> - down_write(&mm->mmap_sem);
> -
> - current->mm->pinned_vm -= diff;
> - up_write(&mm->mmap_sem);
> - mmput(mm);
> + atomic_long_sub(&mm->pinned_vm, diff);
> kfree(umem);
> }
> EXPORT_SYMBOL(ib_umem_release);
> diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
> index f2b81b9ee0d6..16381c6eae77 100644
> --- a/drivers/infiniband/core/uverbs_cmd.c
> +++ b/drivers/infiniband/core/uverbs_cmd.c
> @@ -332,7 +332,6 @@ ssize_t ib_uverbs_get_context(struct ib_uverbs_file *file,
> INIT_LIST_HEAD(&ucontext->ah_list);
> INIT_LIST_HEAD(&ucontext->xrcd_list);
> INIT_LIST_HEAD(&ucontext->rule_list);
> - ucontext->closing = 0;
>
> resp.num_comp_vectors = file->device->num_comp_vectors;
>
> diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
> index 75ad86c4abf8..8fdc9ca62c27 100644
> --- a/drivers/infiniband/core/uverbs_main.c
> +++ b/drivers/infiniband/core/uverbs_main.c
> @@ -196,8 +196,6 @@ static int ib_uverbs_cleanup_ucontext(struct ib_uverbs_file *file,
> if (!context)
> return 0;
>
> - context->closing = 1;
> -
> list_for_each_entry_safe(uobj, tmp, &context->ah_list, list) {
> struct ib_ah *ah = uobj->object;
>
> diff --git a/drivers/infiniband/hw/ipath/ipath_file_ops.c b/drivers/infiniband/hw/ipath/ipath_file_ops.c
> index 6d7f453b4d05..f219f15ad1cf 100644
> --- a/drivers/infiniband/hw/ipath/ipath_file_ops.c
> +++ b/drivers/infiniband/hw/ipath/ipath_file_ops.c
> @@ -2025,7 +2025,7 @@ static void unlock_expected_tids(struct ipath_portdata *pd)
> dd->ipath_pageshadow[i] = NULL;
> pci_unmap_page(dd->pcidev, dd->ipath_physshadow[i],
> PAGE_SIZE, PCI_DMA_FROMDEVICE);
> - ipath_release_user_pages_on_close(&ps, 1);
> + ipath_release_user_pages(&ps, 1);
> cnt++;
> ipath_stats.sps_pageunlocks++;
> }
> diff --git a/drivers/infiniband/hw/ipath/ipath_kernel.h b/drivers/infiniband/hw/ipath/ipath_kernel.h
> index 6559af60bffd..afc2f868541b 100644
> --- a/drivers/infiniband/hw/ipath/ipath_kernel.h
> +++ b/drivers/infiniband/hw/ipath/ipath_kernel.h
> @@ -1083,7 +1083,6 @@ static inline void ipath_sdma_desc_unreserve(struct ipath_devdata *dd, u16 cnt)
>
> int ipath_get_user_pages(unsigned long, size_t, struct page **);
> void ipath_release_user_pages(struct page **, size_t);
> -void ipath_release_user_pages_on_close(struct page **, size_t);
> int ipath_eeprom_read(struct ipath_devdata *, u8, void *, int);
> int ipath_eeprom_write(struct ipath_devdata *, u8, const void *, int);
> int ipath_tempsense_read(struct ipath_devdata *, u8 regnum);
> diff --git a/drivers/infiniband/hw/ipath/ipath_user_pages.c b/drivers/infiniband/hw/ipath/ipath_user_pages.c
> index a89af9654112..8081e76fa72c 100644
> --- a/drivers/infiniband/hw/ipath/ipath_user_pages.c
> +++ b/drivers/infiniband/hw/ipath/ipath_user_pages.c
> @@ -68,26 +68,22 @@ int ipath_get_user_pages(unsigned long start_page, size_t num_pages,
> struct page **p)
> {
> unsigned long lock_limit;
> + struct mm_struct *mm = current->mm;
> size_t got;
> int ret;
>
> - down_write(&current->mm->mmap_sem);
> lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> -
> - if (current->mm->pinned_vm + num_pages > lock_limit &&
> + if (atomic_long_add_return(&mm->pinned_vm, num_pages) > lock_limit &&
> !capable(CAP_IPC_LOCK)) {
> - up_write(&current->mm->mmap_sem);
> ret = -ENOMEM;
> - goto bail;
> + goto bail_sub;
> }
> - current->mm->pinned_vm += num_pages;
> - up_write(&current->mm->mmap_sem);
>
> ipath_cdbg(VERBOSE, "pin %lx pages from vaddr %lx\n",
> (unsigned long) num_pages, start_page);
>
> for (got = 0; got < num_pages; got += ret) {
> - ret = get_user_pages_unlocked(current, current->mm,
> + ret = get_user_pages_unlocked(current, mm,
> start_page + got * PAGE_SIZE,
> num_pages - got, 1, 1,
> p + got);
> @@ -101,9 +97,8 @@ int ipath_get_user_pages(unsigned long start_page, size_t num_pages,
>
> bail_release:
> __ipath_release_user_pages(p, got, 0);
> - down_write(&current->mm->mmap_sem);
> - current->mm->pinned_vm -= num_pages;
> - up_write(&current->mm->mmap_sem);
> +bail_sub:
> + atomic_long_sub(&mm->pinned_vm, num_pages);
> bail:
> return ret;
> }
> @@ -166,56 +161,7 @@ dma_addr_t ipath_map_single(struct pci_dev *hwdev, void *ptr, size_t size,
>
> void ipath_release_user_pages(struct page **p, size_t num_pages)
> {
> - down_write(&current->mm->mmap_sem);
> -
> - __ipath_release_user_pages(p, num_pages, 1);
> -
> - current->mm->pinned_vm -= num_pages;
> -
> - up_write(&current->mm->mmap_sem);
> -}
> -
> -struct ipath_user_pages_work {
> - struct work_struct work;
> - struct mm_struct *mm;
> - unsigned long num_pages;
> -};
> -
> -static void user_pages_account(struct work_struct *_work)
> -{
> - struct ipath_user_pages_work *work =
> - container_of(_work, struct ipath_user_pages_work, work);
> -
> - down_write(&work->mm->mmap_sem);
> - work->mm->pinned_vm -= work->num_pages;
> - up_write(&work->mm->mmap_sem);
> - mmput(work->mm);
> - kfree(work);
> -}
> -
> -void ipath_release_user_pages_on_close(struct page **p, size_t num_pages)
> -{
> - struct ipath_user_pages_work *work;
> - struct mm_struct *mm;
> -
> __ipath_release_user_pages(p, num_pages, 1);
> -
> - mm = get_task_mm(current);
> - if (!mm)
> - return;
> -
> - work = kmalloc(sizeof(*work), GFP_KERNEL);
> - if (!work)
> - goto bail_mm;
> -
> - INIT_WORK(&work->work, user_pages_account);
> - work->mm = mm;
> - work->num_pages = num_pages;
> -
> - queue_work(ib_wq, &work->work);
> - return;
> -
> -bail_mm:
> - mmput(mm);
> - return;
> + if (current->mm)
> + atomic_long_sub(&current->mm->pinned_vm, num_pages);
> }
> diff --git a/drivers/infiniband/hw/qib/qib_user_pages.c b/drivers/infiniband/hw/qib/qib_user_pages.c
> index 57ce83c2d1d9..049ab8db5f32 100644
> --- a/drivers/infiniband/hw/qib/qib_user_pages.c
> +++ b/drivers/infiniband/hw/qib/qib_user_pages.c
> @@ -68,16 +68,13 @@ int qib_get_user_pages(unsigned long start_page, size_t num_pages,
> int ret;
> struct mm_struct *mm = current->mm;
>
> - down_write(&mm->mmap_sem);
> lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>
> - if (mm->pinned_vm + num_pages > lock_limit && !capable(CAP_IPC_LOCK)) {
> - up_write(&mm->mmap_sem);
> + if (atomic_long_add_return(&mm->pinned_vm, num_pages) > lock_limit &&
> + !capable(CAP_IPC_LOCK)) {
> ret = -ENOMEM;
> goto bail;
> }
> - mm->pinned_vm += num_pages;
> - up_write(&mm->mmap_sem);
>
> for (got = 0; got < num_pages; got += ret) {
> ret = get_user_pages_unlocked(current, mm,
> @@ -94,9 +91,7 @@ int qib_get_user_pages(unsigned long start_page, size_t num_pages,
>
> bail_release:
> __qib_release_user_pages(p, got, 0);
> - down_write(&mm->mmap_sem);
> - mm->pinned_vm -= num_pages;
> - up_write(&mm->mmap_sem);
> + atomic_long_sub(&mm->pinned_vm, num_pages);
> bail:
> return ret;
> }
> @@ -135,13 +130,8 @@ dma_addr_t qib_map_page(struct pci_dev *hwdev, struct page *page,
>
> void qib_release_user_pages(struct page **p, size_t num_pages)
> {
> - if (current->mm) /* during close after signal, mm can be NULL */
> - down_write(&current->mm->mmap_sem);
> -
> __qib_release_user_pages(p, num_pages, 1);
>
> - if (current->mm) {
> - current->mm->pinned_vm -= num_pages;
> - up_write(&current->mm->mmap_sem);
> - }
> + if (current->mm)
> + atomic_long_sub(&current->mm->pinned_vm, num_pages);
> }
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 7366e9d63cee..9123bfef1dea 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -57,7 +57,7 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
> hiwater_vm << (PAGE_SHIFT-10),
> total_vm << (PAGE_SHIFT-10),
> mm->locked_vm << (PAGE_SHIFT-10),
> - mm->pinned_vm << (PAGE_SHIFT-10),
> + atomic_long_read(&mm->pinned_vm) << (PAGE_SHIFT-10),
> hiwater_rss << (PAGE_SHIFT-10),
> total_rss << (PAGE_SHIFT-10),
> data << (PAGE_SHIFT-10),
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index d9851eeb6e1d..f2bf72a86b70 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -355,7 +355,7 @@ struct mm_struct {
>
> unsigned long total_vm; /* Total pages mapped */
> unsigned long locked_vm; /* Pages that have PG_mlocked set */
> - unsigned long pinned_vm; /* Refcount permanently increased */
> + atomic_long_t pinned_vm; /* Refcount permanently increased */
> unsigned long shared_vm; /* Shared pages (files) */
> unsigned long exec_vm; /* VM_EXEC & ~VM_WRITE */
> unsigned long stack_vm; /* VM_GROWSUP/DOWN */
> diff --git a/include/rdma/ib_umem.h b/include/rdma/ib_umem.h
> index 9ee0d2e51b16..2dbbd2c56074 100644
> --- a/include/rdma/ib_umem.h
> +++ b/include/rdma/ib_umem.h
> @@ -47,9 +47,6 @@ struct ib_umem {
> int writable;
> int hugetlb;
> struct list_head chunk_list;
> - struct work_struct work;
> - struct mm_struct *mm;
> - unsigned long diff;
> };
>
> struct ib_umem_chunk {
> diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
> index e393171e2fac..bce6d2b91ec7 100644
> --- a/include/rdma/ib_verbs.h
> +++ b/include/rdma/ib_verbs.h
> @@ -961,7 +961,6 @@ struct ib_ucontext {
> struct list_head ah_list;
> struct list_head xrcd_list;
> struct list_head rule_list;
> - int closing;
> };
>
> struct ib_uobject {
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index dd236b66ca3a..80d2ba7bd51c 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3922,7 +3922,7 @@ again:
> */
>
> atomic_long_sub((size >> PAGE_SHIFT) + 1, &mmap_user->locked_vm);
> - vma->vm_mm->pinned_vm -= mmap_locked;
> + atomic_long_sub(&vma->vm_mm->pinned_vm, mmap_locked);
> free_uid(mmap_user);
>
> ring_buffer_put(rb); /* could be last */
> @@ -3944,7 +3944,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
> struct ring_buffer *rb;
> unsigned long vma_size;
> unsigned long nr_pages;
> - long user_extra, extra;
> + long user_extra, extra = 0;
> int ret = 0, flags = 0;
>
> /*
> @@ -4006,16 +4006,14 @@ again:
>
> user_locked = atomic_long_read(&user->locked_vm) + user_extra;
>
> - extra = 0;
> if (user_locked > user_lock_limit)
> extra = user_locked - user_lock_limit;
>
> lock_limit = rlimit(RLIMIT_MEMLOCK);
> lock_limit >>= PAGE_SHIFT;
> - locked = vma->vm_mm->pinned_vm + extra;
>
> - if ((locked > lock_limit) && perf_paranoid_tracepoint_raw() &&
> - !capable(CAP_IPC_LOCK)) {
> + if (atomic_long_add_return(&vma->vm_mm->pinned_vm, extra) > lock_limit &&
> + perf_paranoid_tracepoint_raw() && !capable(CAP_IPC_LOCK)) {
> ret = -EPERM;
> goto unlock;
> }
> @@ -4039,7 +4037,6 @@ again:
> rb->mmap_user = get_current_user();
>
> atomic_long_add(user_extra, &user->locked_vm);
> - vma->vm_mm->pinned_vm += extra;
>
> ring_buffer_attach(event, rb);
> rcu_assign_pointer(event->rb, rb);
> @@ -4049,6 +4046,8 @@ again:
> unlock:
> if (!ret)
> atomic_inc(&event->mmap_count);
> + else if (extra)
> + atomic_long_sub(&vma->vm_mm->pinned_vm, extra);
> mutex_unlock(&event->mmap_mutex);
>
> /*
> --
> 1.8.1.4
>

--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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